[MapProxy] 512x512 tile service from 256x256 tile source

[Radim Blazek]

I would like to get 512x512 tiles from a source which has 256x256
tiles, here is my config:

------------------------------------------------------------------------------------------------------------------------
services:
  tms:
    use_grid_names: true
    srs: ['EPSG:3857']

layers:
  - name: osm
    title: OSM
    sources: [osm_cache]

caches:
  osm_cache:
    grids: [webmercator_512]
    sources: [osm_source]

sources:
  osm_source:
    type: tile
    grid: webmercator
    url: http://tile.openstreetmap.org/%(z)s/%(x)s/%(y)s.png

grids:
    webmercator:
      base: GLOBAL_WEBMERCATOR

    webmercator_512:
      base: GLOBAL_WEBMERCATOR
      tile_size: [512, 512]
      res: [78271.516964, 39135.758482, 19567.879241, 9783.9396205 ]
------------------------------------------------------------------------------------------------------------------------

But this request: /tiles/osm/webmercator_512/0/0/0.png returns: "tile
size of cache and tile source do not match: (256, 256) != (512, 512)"

Making 512x512 tile service from WMS source or higher resolution WMS
service from 256x256 tile source both work.

So what is the trick to get 512x512 tiles?

Radim